Method of coating metal and articles produced thereby



Feb. 6, 1951 J. R. FISHER, JR METHOD OF COATING METAL AND ARTICLES PRODUCED THEREBY Filed Feb. 10, 1947 ZINCILATE COATING NEUTRALIZER MOISTURE IMPERVIOUS COATING SUCH AS,- ALUMINUM PAINT, CHLORINATED RUBBER ZINC FLAKE NEUTRALIZER DECORATIVE COATING INVENTOR JOHN R. F|SHER,JR. BY

r- Jourum/ ATTORNEYS Patented Feb. 6, 1951 UNITED STATES PATENT, OFFICE 'i i 2,546,108 r I METHOD OF COATING .METAL AND ARTICLES PRODUCED THEREBY John R. Fisher, Jr., Dayton, Ohio, :assignor-"to' Industrial Metal Protectives, Inc.,.Dayton, Ohio, a corporation .ofDelaware Application February 10, 1947-, Serial N05727A89 SClaims.

Thisinventiondeals with-a method ofapplying a decorative coating" to a protective coating .of

the metal dust-silicate type and with products obtained thereby.

So-called Zincilate coatings, which are such coatings ofthe metal dust-silicate type, are highlyalkaline, andalkali is exuded to their surface. Decorative coatings applied to such highly alkaline coatings are usually greatly impaired by the alkali, for instance the oils of oil paints are saponified thereby.

It is an object of this invention to provide a combination of protective and decorative coatings and a method of preparing the same which are free from the disadvantage set forth above.

It is another object of this invention to'provide metals witha protective and adecorative coating which both coatings do not react with each other.

It is still another object of this invention. to provide a protectively coated metal with a decorative coating wherein the said decorative coating is not attacked by said protective coating so that it has a relatively long service life.

I It is still another object of this invention to provide metals with a protective and a decorative-coating which are resistant to: salt water, for

instance to sea water. 7

, These and other "objects are accomplished by The protective so-called "Zincilate coating con tains an alkali silicate of a specific gravity of -from 11.28 to 1.30 and-a'NazOgSiOz ratioranging fromll :2.3 to- 1 1 3.0, -a-solub1e chromzttepandmetal 'tlu'st having "particles so small that at least 90% thereof'pass through a-400-mesh Tyler sieve but "preferably of an 'average'particle size o'f-3 microns 'orsmaller. The production and composition of such protective coatings is the subject matter f the copending application Seiial Number 727,490, "filed February 10, 1947, of which the inventor of the 'ihstant application is a co-inventor.

It has been found that various methods' an'cl 'm'aterials'may be used'for obtaining said intermediate coating. Thus, "forexample a neutralizing acid, preferably phosphoric acid, may heapplied. to the alkaline protective coating. In the case of phosphoric aci'd'the alkali is neutralized and thus'rendered harmless, and furthermore the m'et'al'of the protective coating reacts "with the phosphoric "acid under the" formation of an inselubl'einetalfphosphate; Thesereactions, in the 2 case .of -a;zinc containing Zincilate coating, take place according to the following equation H3PO4+3NaOHZ=Na3PO4+3H2O 2I-IsPO4-|-3Zn=Zn3(PO4)z+3H-2 In addition to said phosphoric acid coating, :a further intermediate coating maybe applied. For the preparation of such an additional coating aluminum paint, a chlorinated rubber solution, or a'zinc flake coating were found to be satisfactory. These "additional intermediate coatingsare especially advisable for cases where the metal is to be exposed; to particularly strong attackingor surface corrodingfaotors, forinstance in the case where they are to contact sea water for a considerable period of.,time. The insoluble zinc phosphate obtained with the neutralizer provides for a rather dense and impervious coating and thus prevents moisture that penetrates the pores of the decorative coat- -ing ;from carrying .oil or other acid containing materials from-said decorative coating into the Zincilate layer and thus a reaction between the acid of said decorative coating and the alkali of said Zincilate. However, if the metal articles are to be exposed to highlycorrosive elements such as sea water, the decorative coating is attacked and deteriorates due to alkali of the Zincilate coating still having access to the decorative coat- 'ing. In suchevents, theadditional intermediate coating described above is advisable.

. As the .neutralizer, phosphoric acid is usable; however, an aqueous solution thereof having a concentration of not more than 2% is preferred. Instead "of phosphoric acid, any other low concentrated acid'which .forms an insoluble. salt withthezmetalof the protective :coating; may-, be used. Fertile-additional intermediate coating, :an aluminum paint maybe used which'is based on a conventional varnish :andxwhich contains from '2 to 4. lbs. of aluminum 'flake: per gallon-of varnish. '1

The chlorinated rubber for the additional in termediate coating is preferably used in. the form of a solution; g y

The zinc flake coating is composed similarly to the protectivemetal. dust-silicate coating with ,the exception that-metal flakes are used instead of metal dust. Compositions which were found satisfactory therefor contain: 7

Sodium silicate (sp. g. of about 1.3 and NazOt'sioz ratio-ofabout 1:2.4) gal1ons "-1 Lemma; ests In contradistinction to zinc and other metal in powder form, the flakes of said last-mentioned intermediate coating leaf together and thus provide for a non-porous and impervious layer.

While the aluminum paint and chlorinated rubber coatings are applied after a neutralizer has been placed on the protective coating, a zinc flake coating is advantageously applied immediately on the protective coating and the neutralizer layer placed thereover.

The coatings may be applied by any conventional method known in the art; however, coating by spraying or brushing is preferred. Each kind of coating is immediately subjected to a drying step after application. The paint and rubber coatings have to be air dried or baked and vulcanized, respectively, the temperature of these steps depending upon the kind of compositions used in these coatings. For the zinc flake coating, a baking temperature of from 300 to 700 F. and a baking time for at least 1 hour are advisable.

The process is illustrated in the attached fiow sheet which contains the various modifications set forth above. For the sake of simplicity and clarity, the drying and baking steps which follow each individual coating step have not been included there. Otherwise the flow sheet is selfexplanatory.

Any of the modifications of my process yield coatings in which the protective and decorative layers do not react with each other and in which the decorative coating has an extremely long service life even when exposed to as corrosive a solution as sea water.

It will be understood that while there have been described herein certain specific embodiments of my invention, it is not intended thereby to have it limited to or circumscribed by the specific details given in view of the fact that this claims.

I'claim:

1. In a process for coating metal the steps of depositing a layer of a coating composition comprising a dispersion of zinc dust having an average particle size of about 3 microns, at least 90% of which is capable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali metal silicate containing soluble chromate, the ratio of alkali metal oxide to silica defined in moles being 122.3 to 1 :3.0, setting the zinc dustsilicate coating, applying an acid solution to the set base layer which reacts with the surface of the alkali silicate layer and with thezinc metal therein to form a salt layer, the zinc salt por- .tion of which is insoluble, drying the salt layer,

and thereafter applying an oil base decorative :coating to the dry salt layer.

2. In a process for coating metal the steps of depositing a layer of a coating composition comprising a dispersion of zinc dust having an average particle size of about 3 microns, at least 90% of which is capable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali metal silicate containing soluble chromate, the ratio of alkali metal oxide to silica defined in the moles being 1:23 to 1:3.0, setting the zincdust silicate coating, applying an acid solution to the set base layer which reacts with the surface of the-alkali silicate layer and with the zinc metal therein to form a salt layer, the zinc salt gportionqf ,which is insoluble, drying thesalt layer, thereafter applying oil base decorative coating to the dry salt layer, and baking the' multi-layered finish obtained.

3. In a process for coating metal the steps of depositing a layer of a coatin composition comprising a dispersion of zinc dust, the average particle size of which is not larger than 6 microns and having an average particle size of 3 microns, at least of which is capable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali metal silicate containing soluble chromate, the ratio of alkali metal oxide to silica defined in moles being 1:23 to 113.0, the proportion of alkali metal silicate to zinc dust varying between 25%:75% to 29%:7l% by weight, setting the zinc dust-silicate coating, applying an acid solution to the set base layer which reacts with the surface of the alkali silicate layer and with the zinc metal therein to form a salt layer the zinc salt portion of which is insoluble, drying the salt layer, and thereafter applying an oil base decorative coating to the dry salt layer.

4. In a process for coating metal the steps of depositing on clean metal surface a layer of coating composition comprising a dispersion of zinc dust having an .average particle size of about 3 microns, at least 90% of which is capable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali metal silicate containing alkali metal chromate, the ratio of alkali metal oxide to silica defined in moles being l:2.3 to 1:3.0, setting the zinc dust-silicate layer by heating, treating the set silicate layer with a dilute aqueous solution of phosphoric acid of a concentration less than 2% which reacts with the surface of the alkali silicate layer and with the zinc therein to form a salt layer at least a portion of which is insoluble zinc phosphate, drying the salt layer, and thereafter applying an oil base decorative coating to the dry salt layer.

5. In a process for coating metal, the steps of depositing on clean metal surface a layer of coating composition comprising a dispersion of zinc dust having an average particle size of about 3 microns at least 90% of which is capable of passing through a 400 mesh Tyler sieve in an aqueou solution of an alkali metal silicate containing alkali metal chromate, the ratio of alkali metal oxide to silica defined in moles being 1:23 to 1:3.0, setting the zinc dust-silicate layer by heating, treating the set silicate layer'with a dilute aqueous solution of phosphoric acid of a concentration less than 2% which reacts with the surface of the alkali silicate layer and with the zinc therein to form a salt layer at least a portion of which is insoluble zinc phosphate, drying the salt layer, applying a solution of a chlorinated rubber to said salt layer, dryingand vulcanizing said rubber layer, and thereafter applying an oil base decorative coating -to' the-dry rubber layer.

6. A ferrous metal article having on the surface thereof a hard protective coating resulting from the application thereto and the drying thereon of superimposed layers, the first layer comprising zinc dust of an average particle size of about 3 microns at least 90% of which is ca.- pable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali silicate and alkali chromate, the ratio of alkali metal oxide to silica in the silicate defined in moles being approximately 1:23 to 1:3.0, the second layer of which consists of a dry salt at least a portion of, which is insoluble zinc salt formed by re.-

action of dilute acid on the surface of the zinc dust-silicate layer, and the third layer of which is an oil base decorative coating applied to the dry salt layer.

7. A ferrous metal article having on the surface thereof a hard, protective coating resulting from the application thereto and the drying thereon of superimposed layers, the first layer comprising zinc dust of an average particle size of about 3 microns at least 90% of which is capable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali silicate and alkali chromate, the ratio of alkali metal oxide to silica in the silicate defined in moles being approximately 122.3 to 1:30, a second layer of which consists of a dry salt at least a portion of which is insoluble zinc phosphate formed by the reaction of dilute phosphoric acid of a concentration less than on the surface of the zinc dust-silicate layer, and a third layer of which is an oil base decorative coating applied to the dry salt layer.

8. A ferrous metal article having on the surface thereof a hard protective coating resulting from the application thereto and the drying thereon of superimposed layers, the first layer comprising zinc dust of an average particle size of about 3 microns at least 90% of which is capable of passing through a 400 mesh Tyler sieve in an aqueous solution of an alkali silicate and 6 alkali chromate, the ratio of alkali metal oxide to silica in the silicate defined in moles being approximately 1:23 to 1:3.0, a second layer of which consists of a dry salt at least a portion of which is insoluble zinc phosphate formed by the reaction of dilute phosphoric acid of a concentration less than 2% on the surface of the zinc dust-silicate layer, and the third layer of which is vulcanized chlorinated rubber applied to said dry salt layer, and the fourth layer of which is an oil base decorative coating applied to the rubber layer.

JOHN R. FISHER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,973,740 Andres Sept. 18, 1934 2,076,869 Tanner Apr. 13, 1937 2,088,140 Rosenthal July 27, 1937 2,163,678 Gundlach June 27, 1939 FOREIGN PATENTS Number Country Date 15,131 Australia Aug. 17, 1928 of 1928 

4. IN A PROCESS FOR COATING METAL THE STEPS OF DEPOSITING ON CLEAN METAL SURFACE A LAYER OF COATING COMPOSITION COMPRISING A DISPERSION OF ZINC DUST HAVING AN AVERAGE PARTICLE SIZE OF ABOUT 3 MICRONS, AT LEAST 90% OF WHICH IS CAPABLE OF PASSING THROUGH A 400 MESH TYLER JSIEVE IN AN AQUEOUS SOLUTION OF AN ALKALI METAL SILICATE CONTAINING ALKALI METAL CHROMATE, THE RATIO OF ALKALI METAL OXIDE TO SILICA DEFINED IN MOLES BEING 1:2.3 TO 1:3.0, SETTING THE ZINC DUST-SILICATE LAYER BY HEATING, TREATING THE SET SILICATE LAYER WITH A DILUTE AQUEOUS SOLUTION OF PHOSPHORIC ACID OF A CONCENTRATION LESS THAN 2% WHICH REACTS WITH THE SURFACE OF THE ALKALI SILICATE LAYER AND WITH THE ZINC THEREIN TO FORM A SALT LAYER AT LEAST A PORTION OF WHICH IS INSOLUBLE ZINC PHOSPHATE, DRYING THE SALT LAYER, AND THEREAFTER APPLYING AN OIL BASE DECORATIVE COATING TO THE DRY SALT LAYER. 